Constant periodic motion device



a 5 6 w 3 w! Filed May 25, 1955 wwllhti Allin-l Amp/ifier' INVENTOR.(Jacob Rab/now Attorney United States Patent CONSTANT PERIODIC MOTIONDEVICE Jacob Rabinow, Takoma Park, Md. Application May 25, 1955, SerialNo. 510,941

9 Claims. (Cl. 58-29) This invention relates to high precisiontimepieces of the gravity pendulum type and, more specifically, to atype of pendulum which is driven by another pendulum through a servosystem.

It is well-known that pendulum clocks of extremely high precision havebeen built but even in the best of these it has not been possible toeliminate the effects of the variations in the driving impulsesdelivered to the pendulum and of the friction in the suspension. Thefact that spring suspensions are used does not completely eliminatefriction because of hysteresis in the spring. It is the purpose of thisinvention to eliminate or greatly reduce both the effects of the drivingmechanism on the pendulum and of the variations of the friction in thesus pension of the pendulum.

The specific nature of the invention, as well as other objects andadvantages thereof, will clearly appear from a description of apreferred embodiment as shown in the accompanying drawing, in which:

Fig. l is a schematic diagram showing the basic arrangement of my doublependulum clock, partly in section; and

Fig. 2 is a side view of the double pendulum clock and some additionaldetails.

The pendulum 2 is contained within another pendulum 3 and the two swingtogether as will be described below. The axes of the two pendulums aremade colinear. This can be done in many ways, but the method shown is tohang the outer pendulum on two knife edges 4, 6. The inner pendulum ishung on another knife edge 7 and the axes of rotation of both sets ofknife edges are made as closely aligned as possible. The outer pendulumis provided with two small windows near its lower end shown at 8 and 9.These windows are so located that when the inner pendulum and the outerpendulum hang still, the windows are just half covered by the bob 11 ofthe inner pendulum.

The periods of the two pendulums are independently made to be as nearlyequal as possible. The outer pendulum is driven by the best availablemeans, for example, such as described in Dr. Rawlins book on The Scienceof Clocks and Watches," second edition, page 108. Schematically themechanism is shown in Fig. 1.

The outer pendulum is driven by an unbalanced weight 15 pivoted aboutthe point 12. As the pendulum swings to the right as seen in Fig. 1, itcontacts the lower end of this weight, closing the circuit through thebattery and the two electromagnets 13 and 14 (see Fig. 2). Prior to thisinstant, the rocking armature of the solenoid was held against the pin17 by the action of the spring 18. For this purpose the outer casing ofouter pendulum 3 is assumed to be made of conducting material, althoughin practice it would probably be preferable to specially form thecircuit closing path of the pendulum as a switching strip attached tothe pendulum. It will be understood that points x-x in Fig. 1 areconnected to points xx in Fig. 2, in accordance with usual circuitdrawing practice. The pendulum touching the unbalanced weight 15 notonly closes the circuit by direct contact, as mentioned earlier, butalso lifts the right hand supporting finger 19 of this weight from theplatform 21. The current flowing through the solenoid 13 tilts theplatform into the position shown in Fig. 1. The pendulum continues itsswing to the right, comes to a stop and then begins its swing to theleft. The contact between the pendulum 3 and the weight 15 will bebroken at a point later in the cycle than it was made. Or in otherwords, the weight will stay in contact with the pendulum for a longertime on the down stroke than it was on the up stroke. This impartsenergy to the pendulum and maintains its oscillations. After the contactis broken, the solenoid 13 releases, permitting the armature 21 to swingagainst the pin, lifting the unbalanced weight and thus recocking it forthe next cycle.

It will be obvious to those versed in the art of such mechanisms that ifthe outer pendulum is caused to swing, the inner pendulum will begin toswing also, due to the coupling between them produced both by the aircontained in the outer pendulum and by the very small friction in theinner bearings. Even if the outer pendulum were completely evacuated andno air coupling were present, the small amount of friction inevitablypresent in the suspension of the inner pendulum would cause thispendulum to oscillate at some time after the outer pendulum werestarted. Methods of locking both pendulums together at the start can, ofcourse, also be used but have no significant bearing on the crux of thisinvention. A photocell 22 and a source of light 23, which may be anelectric light bulb, are mounted on opposite sides of the main pendulumas shown in Fig. 2. If both pendulums swing in exact synchronism, thewindows will be half covered by the bob of the inner pendulum and asmall amount of light would reach the photocell if the light bulb wereenergized. The light bulb is controlled by a cam wheel 24 which isoperated by electromagnet 14 connected in series with the electromagnet13 that operates the mechanism driving the outside pendulum. A pawlspring 25 advances the cam wheel 24 one tooth each time the magnet 14 isenergized. It will be seen that during every stroke of the pendulum 3,as its electromagnet moves the armature 21, the cam wheel is advancedone step. During the motion of the cam wheel the contact 26 closes andopens, thus lighting the bulb once per complete oscillation of thependulum. By properly locating the cam follower with respect to the camwheel, the light bulb can be made to light at approximately the timewhen the outside pendulum swings through its neutral point. It will beseen that the contact is closed only when the pendulum swings in onedirection. The timing of the light is not critical since the phasing ofthe pendulum does not change appreciably through a small portion of anyone stroke.

The light falling on the photocell produces a current impulse in thelatter which is fed to the amplifier 27, points Y-Y of Figs. 1 and 2being connected in the same circuit. The amplifier is so arranged thatit produces an output which is substantially a direct current whosevalue is proportional to the intensity of the pulses. Means forproducing a smooth direct current whose intensity varies with theintensity of the pulsed input of the amplifier are well-known to theelectronic art and are described, for example, on pages 482-500 of RadioEngineering by Terman, 2nd ed. (McGraw-Hill). The direct current of theamplifier 27 is fed to a balanced armature relay 28 whose other side isbiased by direct current such as obtainable from a battery 29. The relay28 is a single-pole double-throw relay which stays in neutral when thecurrents through its two windings are equal.

A direct current, reversible, motor 31 is connected to the output ofrelay 28 and is arranged through gearing 32 to raise and lower a smallpermanent magnet 34 mounted below the outside pendulum. A small piece ofmagnetic material 36 is shown mounted on the pendulum. It will be seenthat the position of the permanent magnet will affect the rate of thependulum. Weight 37 is located near the bottom of pendulum 3 so that thecenters of gravity of both pendulums are substantially coaxial.

it is now obvious that by proper adjustment of the output relay currentsin relay 28, the condition can be set up where if the two pendulums movein unison, the intensity of the light pulses falling on the photocellwill be such as to produce equilibrium in the output relay and keep themotor from turning. If the outer pendulum 1 is not in phase with itsinner counterpart, the light pulses will be either larger or smallerdepending on the phase relationships of the two pendulums, the currentsin the output relay will be unbalanced, the motor will run in theappropriate direction to change the rate of the outer pendulum and bringthe two pendulums into synchronism again. By making the windows in theouter pendulum very narrow the sensitivity of such a device can be madevery high. The mechanical arrangement of the magnetic speed adjustmentis such as to cause very slow changes in the rate of the outer pendulumso that small perturbations in the oscillations of the two pendulumswould have little eifect on the overall adjustment.

It is obvious that the amplitude of the oscillations of the outsidependulum can be varied, if desired, by means well-known to the art. Onemethod of accomplishing changes in amplitude would be to move theposition of the stop pin 17 so as to increase or decrease the energyimparted to the outer pendulum during each cycle.

It will be seen that if the two pendulums are moving in exactsynchronism the inner pendulum experiences negligible losses. It movesin unison with the outer pendulum and, if the outer pendulum isevacuated, there are no losses due to air friction. Even if the outerpendulum were not evacuated, the losses due to air friction would begreatly reduced because both pendulums are swinging together carryingthe air with them. The air losses would be merely due to some secondarycirculating currents. In electrical terms, therefore, the losses of theinner pendulum are much reduced, its Q is greatly increased, and itsaccuracy should be proportionately improved. If one assumes, forexample, that the two pendulums move one inch at their lower extremityand if one assumes further that the servo system is good enough to keepthem in step within 0.001 of an inch, then the losses of the innerpendulum are reduced by a factor of the order of 1000 and its Qincreased several orders of magnitude.

It is obvious that the method of reducing losses by driving the bearingsof a moving member in synchronism with the member are also applicable todevices other than a gravity pendulum. It should be recognized that theuse of the outer pendulum is merely a convenient way of oscillating theknife edge bar supporting the inner pendulum.

While the suspension described so far is of the knife edge variety, I donot intend to be limited by this description. Either pendulum can besuspended by a spring or any other device without departing from thesense of my invention. While it is desirable to keep the axes ofrotation as nearly colinear as possible, slight deviation from this canbe tolerated because the effect of such small deviation would be tomerely cause the inner 4 pendulum to move a very small amount verticallyas the two pendulums swing from side to side.

It will be apparent that the mechanism shown may be incorporated into aclock or other timepiece as the time reference element thereof, e. g.,the outer pendulum 3 may be substituted for the pendulum of anypendulumcontrolled clock.

It will be apparent that the embodiment shown is only exemplary and thatvarious modifications can be made in construction and arrangement withinthe scope of my invention as defined in the appended claims.

I claim:

1. A mass mounted on an axis for periodic motion about said axis, abearing supporting said mass for said motion, said bearing comprising asupporting portion movable about said axis with respect to said mass,means for imparting periodic motion to said supporting portion aboutsaid axis, means for sensing the periodic motion of said mass withoutappreciably disturbing said motion and producing signals related to saidmotion, and means controlled by said signals for maintaining theperiodic motion of said supporting portion synchronized with theperiodic motion of said mass to minimize relative motion between saidbearing portion and said mass.

2. The invention according to claim 1, said mass being a pendulum.

3. The invention according to claim 2, said means for sensingcomprisingan optical sensing system.

. ing of an oscillating member, supporting means for said oscillatingmember free to oscillate in unison with the oscillations of saidoscillating member, means to oscillate said support means, and furthermeans to detect the motion of said oscillating member and to oscillatesaid support means in phase with said oscillating memher.

6. In a timing device, a periodic actuating means, a first pendulumdriven by said means, a second pendulum supported for independentoscillation by said first pendulum, means for detecting difierences inmotion between said pendulums, and means controlled by said detectingmeans for affecting said periodic actuating means to maintain a constantphase relationship between said pendulums.

7. The invention according to claim 6, said second pendulm being mountedwithin said first pendulum.

8. The invention according to claim 7, said first pendulum totallyenclosing said second pendulum.

9. The invention according to claim 6, said means for detectingdifierences comprising photoelectric means.

References Cited in the file of this patent UNITED STATES PATENTS1,523,149 Wheeler Jan. 13, 1925 1,595,170 Schieferstein Aug. 10, 19261,868,769 Schuler July 26, 1932 1,998,727 Le Rolland Apr. 23, 19352,632,292 Amend, Jr. Mar. 24, 1953

